The Simple Explanation

Wastewater Treatment Removes Solids, Organic Matter, Nutrients and Harmful Contaminants.

Wastewater arriving at a treatment plant is not cleaned in a single process.

Instead, it normally passes through a sequence of mechanical, physical, biological and sometimes chemical treatment stages.

Large debris is removed first, heavier solids are allowed to settle, microorganisms break down dissolved organic material and further treatment can then reduce nutrients, pathogens and remaining contaminants.

The exact process varies between facilities, but the overall objective is the same: reduce pollution sufficiently for the treated water to be safely discharged or reused for an appropriate purpose.

Understanding Wastewater

What Is Sewage Wastewater?

Sewage wastewater is the used water leaving homes, commercial buildings and industrial premises.

Domestic wastewater can contain human waste, food particles, detergents, soap, grease, nutrients and microorganisms generated through everyday activities such as washing, cooking, cleaning and toilet use.

Industrial wastewater can be much more varied. Depending on the activity involved, it may contain oils, metals, chemicals or other contaminants requiring specialist treatment.

In some drainage systems, surface-water runoff can also carry dirt, hydrocarbons and other pollutants from roads and hard surfaces into the wider water environment.

Stage One

Screening Protects the Rest of the Treatment Plant.

The first stage removes the largest materials entering the treatment works.

Wastewater passes through metal screens or bars designed to capture items such as plastics, rags, wipes, pieces of wood and other solid debris.

Removing these materials early helps prevent damage to pumps, valves and other treatment equipment further through the process.

It also reinforces why wipes and household rubbish should never be flushed into a toilet in the first place.

Stage Two

Primary Treatment Separates Settling and Floating Material.

After screening, the wastewater enters large settlement tanks.

Flow is slowed so heavier suspended solids can settle to the bottom of the tank, creating sludge.

Lighter substances such as fats, oils and grease can rise towards the surface, where they can be removed separately.

The wastewater leaving primary treatment is cleaner, but significant dissolved organic material and microorganisms remain and require further treatment.

Stage Three

Secondary Treatment Uses Microorganisms to Break Down Organic Waste.

Physical settlement alone cannot remove all the dissolved organic material present in wastewater.

Secondary treatment therefore uses biological processes. In many systems, oxygen is introduced to support communities of microorganisms that feed on organic pollutants.

As these microorganisms consume the organic material, additional biomass or sludge is created.

The treated water then passes through further settlement so the biological solids can be separated from the liquid.

Stage Four

Tertiary Treatment Provides the Final Level of Cleaning.

Where a higher standard of treated water is required, additional processes can be used after biological treatment.

These may target remaining suspended solids, nitrogen, phosphorus, microorganisms or other contaminants that have not been sufficiently removed during the earlier stages.

Treatment may include filtration, disinfection or other specialist processes depending on the quality requirements of the final discharge.

Ultraviolet treatment, for example, can be used to reduce pathogens without adding a residual disinfectant to the water.

Nutrients & Ecosystems

Why Are Nitrogen and Phosphorus a Problem?

Nitrogen and phosphorus are natural nutrients, but excessive quantities entering rivers, lakes and other water bodies can upset the ecological balance.

High nutrient levels can encourage excessive algae growth.

As algae and other organic material die and break down, oxygen can be consumed from the surrounding water, placing fish and other aquatic organisms under stress.

That is one reason nutrient removal can become an important part of advanced wastewater treatment.

Energy Recovery

Can Sewage Treatment Generate Energy?

Yes. Wastewater treatment produces sludge containing significant amounts of organic material, and that material can be used as an energy source.

One common approach is anaerobic digestion. Sludge is placed into enclosed digesters where microorganisms break down organic matter without oxygen.

This process produces biogas containing methane, which can be captured and used to generate heat or electricity.

Energy recovery can reduce the amount of external power required to operate a treatment works.

Other Treatment Options

Are There Alternatives to a Conventional Treatment Plant?

Yes. The most appropriate method depends on the volume and type of wastewater, available land, discharge requirements and whether connection to a mains sewer is practical.

Smaller communities and individual properties may use decentralised systems, while specialist applications can employ advanced filtration and treatment technologies.

Examples include constructed wetlands, membrane filtration, septic tanks and packaged sewage treatment systems.

Each option has different space, maintenance, energy and water-quality requirements.

Off-Mains Drainage

What Happens Where There Is No Mains Sewer?

Not every property sends wastewater to a large municipal treatment works.

Rural homes, agricultural properties, commercial sites and remote developments may rely on their own wastewater infrastructure.

Depending on the site, this might involve a septic tank, sewage treatment plant, cesspit or another approved off-mains drainage solution.

These systems require appropriate design, installation, emptying and maintenance if they are to continue working effectively and protect the surrounding environment.

Need Wastewater or Drainage Help?

Talk to KD Drainage.

KD Drainage works with domestic, commercial and larger sites on sewage systems, wastewater infrastructure, septic tanks, treatment plants, pump stations and general drainage.

Whether you have an existing system that needs attention or require advice about an off-mains drainage solution, our team can help.